The specific aims of this study are concerned with the determinations of the following: (1) the effect of strontium (Sr) and other trace elements on the formation of synthetic apatities; (2) their effect on the dissolution properties of syn. apatites when they are present in the apatite or when the acid media; (3) their effect on the dissolution properties of enamel and dentine; (4) the morphological and compositional changes of enamel surface after exposure to acid media of varing levels of Sr or Sr + F; (5) the effect of acid exposure on the composition and 'crystallinity' of synthetic and biological apatities; (6) the properties of dentine mineral; (7) the nature of the 'central dark zones' (CDZ) associated as the site of dissolution of enamel apatite crystals; (8) the effect of fluoride on the incorporation of de-stabilizing elements (e.g., Mg2+, CO32-, HPO42-) in apatites. Synthetic apatites will be prepared in the presence of Sr and other trace elements by precipitation or hydrolysis methods. Biological samples will include enamel and dentine from extracted caries-free human teeth. Dissolution experiments will be by suspension of the apatites in acetate buffer (O.1M KAc, pH5, 37degreesC, exposure times, 10 to 120 min); extent of dissolution to be expressed as mM Ca or mM P in the acid buffer. X-ray diffraction, infrared absorption spectroscopy, Scanning Electron Microscopy, High-resolution TEM, thermogravimetry, atomic absorption and colorimetry will be used for characterization and analyses. Results from this study will provide information which will: (i) clarify and resolve the conflicting reports on the 'cariostatic' action of Sr- whether topical, systematic, or only in combination with fluoride; (ii) provide insights into the possible mechanisms for the role of other trace elements on the formation and stability of apatites; (iii) provide new information on the properties of the dentine mineral; (iv) provide additional mechanism by which fluoride contribute stability to the bone and tooth mineral. On practical applications, the information forthcoming from this study could be useful in formulation of topical agents (with/without F) for preventive dentistry and possible biomaterials for medical and dental uses.